The formation of alcoholates of anhydrous metal halides has been documented in the literature, and the separation of organic mixtures by formation of metal complexes has been reported. See Sharpless et al, J. Org. Chem., Vol. 40, No. 9, pp 1252-1257(1975). Sharpless et al teach the use of divalent metal salts, particularly the salts of calcium and manganese in the resolution of alcohol mixtures by preferential complexation by calcium chloride or manganese chloride with one alcohol of the mixture, using catalytic amounts of ethanol to enhance the complexing ability of metal halides. The Sharpless et al resolutions are restricted to simple alcohols.
Weber et al. U.S. Pat. No. 4,057,541 disclose a process for isolating 3-hydroxy steroids and 3-keto steroids from mixtures thereof by dissolving the mixtures in an organic solvent, mixing the dissolved mixture with calcium bromide to form insoluble adducts of the steroids, separating the insoluble adducts and splitting the adducts to regenerate the free steroid. Methyl isobutyl ketone and/or methyl n-amyl ketone is used as the solvent.
Weber et al. specifically teach away from the use of metal salts other than calcium bromide (in its hydrate form) stating at Column 2, lines 32-34 "The use of other metal salts which are otherwise suitable for adduct formation also leads to poorer results as compared to the method of the present invention."
It has now been found that a number of organic compounds, particularly pharmaceutical compounds with complex structures i.e., prostaglandins, steroids, antibiotics, etc., which are generally difficult to isolate and purify, are readily and advantageously isolated and purified by the use of complexation of the crude product or reaction mixture with a lithium salt selected from the group consisting of lithium bromide, lithium iodide, lithium perchlorate, and lithium fluoroborate in the presence of a suitable solvent.